When using the map editor I get really odd behavior when placing tiles.

Say I'm placing human wall tiles and I put an extra one and I want to "clear" it by placing a grass tile over it - when I do that I get randomly anywhere from 3-12 grass tiles placed all over the "cleared" tile as well as over adjoining tiles. This makes it impossible to use the editor since every wrong placement equals about a dozen other wrong tiles that each follows the same random rules when I try to "clear" them.

Now I have not used the BNE version yet .

Has anyone encountered this problem or has any idea whats causing it or how it can be fixed?